Water uptake is independent of the inferred composition of secondary aerosols derived from multiple biogenic VOCs
Water uptake is independent of the inferred composition of secondary aerosols derived from multiple biogenic VOCs
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DOI：
10.5194/acp-13-11769-2013
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发表时间：
2013-01-01
影响因子：
6.3
通讯作者：
McFiggans, G.
中科院分区：
文献类型：
--
作者：
Alfarra, M. R.;Good, N.;McFiggans, G.
我们表明，来自分和超饱和测量室产生的生物次生有机气溶胶（SOA）颗粒的吸水性能是独立的氧化程度，确定使用在线和离线的方法。SOA颗粒是由五种结构不同的生物源VOC的光氧化形成的，代表了广泛的排放物质及其相应的化学反应性范围：α-蒎烯，β-香芹烯，柠檬烯，月桂烯和芳樟醇。质量碎片44对总有机信号的分数贡献（f（44））用于表征通过气溶胶质谱仪在线测量的所形成的SOA的氧化程度。结果表明，f（44）值与前体物质、光化学老化程度以及初始实验条件有关。因此，由单一生物前体产生的SOA不应被用作生物SOA的一般代表。类似地，所产生的SOA颗粒表现出一系列吸湿特性，这取决于前体、其初始混合比和光化学老化。所形成的SOA颗粒的活化行为不显示与光化学老化的时间趋势。在两种不同的初始混合比条件下，通常发现来自HTDMA和CCNc的平均kappa值覆盖每种前体的相同范围。α-蒎烯、β-香芹烯、芳樟醇和月桂烯的吸湿性与f（44）之间存在正相关关系，但柠檬烯SOA的吸湿性与f（44）之间不存在正相关关系。对这种关系的一般性的研究表明，α-蒎烯、柠檬烯、芳樟醇和月桂烯都能够产生具有相似吸湿性（κ（HTDMA）类似于0.1）的颗粒，尽管f（44）表现出相对宽的值范围（类似于4至11%）。类似地，kappa（CCN）被发现与f（44）无关。当SOA的亚饱和和超饱和吸水特性与使用离线方法确定的平均碳氧化态（（OSC）棒）进行比较时，同样的发现也是真实的。这些发现并不一定表明水分吸收和化学成分无关。相反，他们认为f（44）和OSC并不代表控制SOA颗粒吸水的主要成分相关因素，或者他们可能强调半挥发性化合物对限制当前最先进技术确定气溶胶颗粒化学成分和吸水特性的能力的可能影响。
We demonstrate that the water uptake properties derived from sub- and super-saturated measurements of chamber-generated biogenic secondary organic aerosol (SOA) particles are independent of their degree of oxidation, determined using both online and offline methods. SOA particles are formed from the photooxidation of five structurally different biogenic VOCs, representing a broad range of emitted species and their corresponding range of chemical reactivity: alpha-pinene, beta-caryophyllene, limonene, myrcene and linalool. The fractional contribution of mass fragment 44 to the total organic signal (f(44)) is used to characterise the extent of oxidation of the formed SOA as measured online by an aerosol mass spectrometer. Results illustrate that the values of f(44) are dependent on the precursor, the extent of photochemical ageing as well as on the initial experimental conditions. SOA generated from a single biogenic precursor should therefore not be used as a general proxy for biogenic SOA. Similarly, the generated SOA particles exhibit a range of hygroscopic properties, depending on the precursor, its initial mixing ratio and photochemical ageing. The activation behaviour of the formed SOA particles show no temporal trends with photochemical ageing. The average kappa values derived from the HTDMA and CCNc are generally found to cover the same range for each precursor under two different initial mixing ratio conditions. A positive correlation is observed between the hygroscopicity of particles of a single size and f(44) for alpha-pinene, beta-caryophyllene, linalool and myrcene, but not for limonene SOA. The investigation of the generality of this relationship reveals that alpha-pinene, limonene, linalool and myrcene are all able to generate particles with similar hygroscopicity (kappa(HTDMA) similar to 0.1) despite f(44) exhibiting a relatively wide range of values (similar to 4 to 11 %). Similarly, kappa(CCN) is found to be independent of f(44). The same findings are also true when sub-and super-saturated water uptake properties of SOA are compared to the averaged carbon oxidation state ((OSC) over bar) determined using an offline method. These findings do not necessarily suggest that water uptake and chemical composition are not related. Instead, they suggest that either f(44) and OSC do not represent the main dominant composition-related factors controlling water uptake of SOA particles, or they may emphasise the possible impact of semi-volatile compounds on limiting the ability of current state-of-the-art techniques to determine the chemical composition and water uptake properties of aerosol particles.